Study And Design Of Wideband Filter For Human Body Communication

With the crossing and integration of electronic information, biological science and other fields,the body network communications technology based on the human body medium has became a new research field. In order to suppress the high-frequency electromagnetic interference from wireless environment as well as ECG, EMG, EEG, and other low-frequency bioelectrical interferences from the body medium, the multi-stage filter with high shape factor is required for improving the quality of the receiving system. In addition, for the future multinode, multi-channel, high-speed and other applications as well as portable or implantable applications, a low-power active multi-stage filter circuit with a wide passband of 100 MHz, which is used before broadband high gain amplifier circuit to improve the signal-to-noise ratio(SNR) of the receiving system is needed to study.For portable or implantable requirements of low power and high-speed in human body communication system, a low power wideband current differencing buffer amplifier(CDBA) was studied. Further, based on the CDBA, a low power wideband high-order filters applied in human body communication system was designed. The main work can be summarized as follows.(1)A novel small signal analysis calculation method of MOS analog integrated circuit was proposed. A model for multi-terminal control feedback system was proposed. Meanwhile, the relationship between the output signal and the input signal was derived theoretically. The output expression derived was consistent with the output expression of the general control feedback system in the form and physical meaning. Furthermore, MOS transistor could be abstracted into a multi-terminal amplifier. Based on this model, the analog integrated circuit can be easily analyzed from the perspective of system. Above all, the transfer functions, input impedance, output impedance or other small signal parameters can be figured out quickly.(2)A low power wideband CDBA was designed. A combined structure of the flipped voltage follower current sinker(FVFCS) and cascade current source was adopted in the input stage of current, and a cascade current mirror was used in the output stage of current. Therefore, it ensures the current transfer accuracy, broaden the current transmission bandwidth and reduce the power consumption. Based on 180 nm CMOS process, the simulation results of the proposed CDBA showed that the current bandwidth of-3dB was 508 MHz, the voltage bandwidth of-3d B was 263 MHz and the power consumption of the whole CDBA was 219μW under a supply voltage of ±0.9 V.(3)Based on the proposed CDBA and the large time constant integrator structure of CDBA, A new highly integrated multiple-loop high-order filter was designed. Based on 180 nm CMOS process, the simulation results showed that the filter bandwidth of-3dB was 1 M~105 MHz, stop-band ratio was 62dB@100KHz and 90dB@1GHz,the power consumption of the filter was 1.6mW. Therefore, the performance of the filter can meet the requirement of the power consumption and bandwidth in human body communication system.